Engraved plastic article

ABSTRACT

An engraved plastic article is prepared by applying a coat of epoxy resin paint to a polyether sulfone resin article, curing the coated article at an elevated temperature, and engraving indicia on a surface of the article. During engraving the paint coating does not loosen, chip or otherwise dislodge.

This invention relates to a process for preparing plastic articlesbearing engraved indicia thereon. More particularly, it relates to aprocess for preparing epoxy paintcoated polyether sulfone resin articlesbearing fine and detailed engraved indicia thereon.

It is well known that display signs, nameplates and other productshaving a plastic substrate and an acrylic sheet laminated thereon, maybe engraved for various applications, so that the substrate showsthrough cut-away portions of the acrylic lamination to show indicia orthe like. However, the process of engraving acrylic extruded laminateplastic articles is not suitable when legible indicia having an engraveddepth and height of significantly less than 0.035 inches and 0.08inches, respectively, are desired. Moreover, the process of laminationoften requires a number of extruding steps, and is thus, relativelyexpensive and complex. It would be desirable to provide a less costlyand complex manufacturing process for preparing engraved plasticproducts. The coating of a plastic substrate with a paint, prior toengraving, has been a simple and relatively inexpensive alternative whenfine and detailed engraving is not required and when irregularly shapedarticles are not used.

Plastic articles having a coating of paint already have widespreadapplications. For example, microphone housings are often formed of aplastic material which has been coated with paint. It is well known thatparticular indicia may be engraved on the surface of such paintedplastic articles to remove the paint coating in order to uncover thesubstrate and thereby identify, inter alia, such items as the source ofmanufacture, the model number, and other features of products withinsuch housings. However, in many instances, fine and detailed engravingof paint-coated plastic has been accompanied by the loosening orchipping of the coated paint. This is undesirable since it adverselyaffects the appearance of the coated product and in addition, preventsmanufacturers from clearly identifying product features by engraving.This chipping or loosening problem, has been avoided to date only by theimplementation of expensive technology. However, even the utilization ofsuch expensive technology has become more difficult and is undesirablewhen plastic parts having curved surfaces or irregular shapes or sizesare used.

It is an object of the present invention to provide a new and relativelyinexpensive process for preparing a paint-coated plastic articlepermitting fine and detailed engraving thereon.

It is another object of this invention to provide a process forpreparing an engraved paint-coated plastic on which the paint does notdislodge after engraving.

It is a further object of this invention to use, in such a process, aplastic substrate which can withstand relatively high temperaturespermitting attaining a good paint-to-substrate bond.

It is another object of the present invention to provide a processusable on plastic substrates of various shapes and sizes, and inparticular substrates having curved surfaces.

It is yet a further object of the present invention to provide anengraved article which is prepared by the above-described process.

In accordance with the present invention, an article made from apolyether sulfone resin is first coated with an epoxy paint material andis then cured at an elevated temperature to form a durable bond betweenthe epoxy paint and the polyether sulfone substrate. Indicia are thenengraved on the surface of the article by cutting both through the paintcoating and into the polyether sulfone substrate. Engraving may beachieved by conventional rotary engraving tools.

It is believed that molecular bonding between the substrate and thepaint occurs during the curing step. It is also believed that theproblem of paint chipping is avoided as a result of this molecularbonding. In contrast to other plastics, polyether sulfone resins areadvantageously capable of withstanding the elevated temperatures (i.e.temperatures approaching the vicat softening point of the resin) whicheffectuate the desirable molecular bonding.

While other polyether sulfone resins may be suitable for the purposes ofthis invention, it is preferred that a polyether sulfone resin substratebe used which is represented by the formula: ##STR1## wherein nrepresents the number of repeat units in the linear polymer. This typeof polyether sulfone resin substrate is particularly desirable since itpossesses improved chemical resistance and impact properties and is alsocapable of withstanding relatively high temperatures which produceenhanced bonding of the epoxy paint.

Paint containing an epoxy-resin component and at least one color pigmentis applied to the polyether sulfone substrate. While spray applicationof the epoxy paint is preferred, in order to provide a thin coat ofpaint, other forms of application may be suitable. The paint may alsoinclude a reducer component which contains volatile alcohol and ketonecompounds. The volatile reducer compounds are effective in thinning theepoxy paint to facilitate forming a thin coat.

The coated polyether sulfone substrate is then cured in a standardconvection oven at a temperature of from about 380° F. to 450° F. for aperiod of 20 to 30 minutes. When the preferred polyether sulfone resinof the above-identified formula is used, the curing temperature shouldbe from about 410° F. to about 425° F., and most preferably should be425° F. The cured epoxy paint should have a hardness of from about 3H toabout 6H, and preferably about 6H. The hardness may be tested inaccordance with the pencil hardness test, ASTM test designationD-3363-74. Fine and detailed indicia including, inter alia, words,logos, and numbers, may be engraved in this way on the surface of thecoated substrate.

The following example is presented to more fully illustrate the presentinvention.

EXAMPLE

An irregularly shaped microphone housing part having curved surfaces wasprepared from a polyether sulfone resin of the formula ##STR2## which isavailable from Imperial Chemical Industries, Materials Business Group,Wilmington, Del. 19897, as VICTREX PES 4800 G. A black epoxy-resinpaint, available from Egyptian Lacquer Manufacturing Company, Inc., 555Sagamore Parkway South, P.O. Box 4449, Lafayette, Ind. 47903, and havingproduct designation ED-L 2245, was sprayed on the microphone housingpart to form a thin coat thereon. This paint contains, inter alia, a BISphenol A type epoxy resin, a butylated urea formaldehyde resin, and acarbon black pigment. The epoxy-resin paint was mixed with a reducercomponent (which is also available from the Egyptian LacquerManufacturing Company, Inc., as RD-L 107), prior to its deposition onthe housing part. The reducer component contains various volatilematerials including alcohols and ketones. The coated housing part wasthen cured in a convection oven at a temperature of 425° F. for a periodof 20 to 30 minutes. The cured epoxy paint had a hardness of 6H. Astandard engraving tool was then used to engrave fine and detailedindicia, including words, logos and numbers, on a curved surface of thecoated housing part. The indicia had a depth of from about 0.0005 inchesto about 0.0012 inches, a width of .015 inches to .025 inches, and acharacter height of from about 0.037 inches to about 2.96 inches. Uponvisual inspection of the engraved housing part, no chipping or looseningof the paint coating occurred. The engraved indicia had sharp edgessupplying excellent definition for the indicia.

The foregoing example illustrates an embodiment of the presentinvention. Many modifications thereof may be made without departing fromthe spirit and the scope of the invention, which is defined by thefollowing claims.

What is claimed is:
 1. An article bearing engraved indicia thereoncomprising:a polyether sulfone resin substrate; a coating of an epoxyresin paint material which has been deposited on a surface of thesubstrate and then cured at an elevated temperature to form a bondbetween the paint material and the substrate layer; said cured andcoated substrate having indicia engraved through the paint material andinto a surface of the substrate.
 2. An article as described in claim 1wherein the coated polyether sulfone resin substrate is cured at atemperature of from about 380° to 450° F.
 3. An article as described inclaim 1 wherein the substrate is a polyether sulfone resin linearpolymer represented by the formula ##STR3## in which n represents thenumber of repeat units in the polymer.
 4. An article as described inclaim 3 wherein the coated substrate is cured at a temperature of fromabout 410° F. to about 425° F.
 5. An article as described in claim 1wherein the engraved indicia have a depth of from about 0.0005 inches toabout 0.0012 inches.
 6. An article as described in claim 1 wherein theengraved indicia have a width of from about 0.015 inches to about 0.025inches.
 7. An article as described in claim 1 wherein the engravedindicia have a height of from about 0.37 inches to about 2.96 inches. 8.An article as described in claim 1 wherein the surface of the substrateis curved.
 9. An article as described in claim 1 wherein the hardness ofthe epoxy resin paint material after curing, is from about 3H to 6H.